Stents are used to maintain the patency of bodily vessels such as coronary, mesentery, peripheral, or cerebral vasculature, veins, the gastrointestinal tract, the biliary tract, the urethra, the trachea, hepatic shunts and fallopian tubes. Stents are delivered to desired locations in bodily vessel via catheters. Examples of catheters are disclosed in U.S. Pat. Nos. 5,772,669 and 6,036,697.
A schematic illustration of a prior art catheter is shown generally at 100 in FIG. 1. Catheter 100 comprises inner tube 104, stent 108 disposed about inner tube 104 toward the distal end of the catheter and retractable sheath 114 which is disposed about stent 108. Retractable sheath 114 is maintained in place over stent 108 during stent delivery to protect the bodily vessel from the stent and to generally facilitate stent delivery. Pull collar 115 is affixed to retractable sheath 114 and pull wire 113 extends proximally from pull collar 115. Upon delivery of stent 108 to the desired location, retractable sheath 114 may be retracted by pulling on pull wire 113. The stent may thus be exposed for expansion and implantation in the desired region of the vessel. Other types of retraction mechanisms are also known in the art.
Subsequent to loading a stent in the catheter, the retractable sheath may dimple or become partially embedded in portions of the stent, in particular where the stent is self-expanding. As shown in FIG. 1, portions 117 of retractable sheath 114 protrude in between struts 116 of stent 108 hampering the retraction of the sheath from over the stent and risking damage to the stent.
The problems of dimpling and/or embedding of the stent are exacerbated as thinner sheaths are used. While it is desirable to employer thinner retractable sheaths to ensure flexibility of the catheter in the region of the retractable sheath and to maintain a low catheter profile, the use of thinner sheaths increases the likelihood of dimpling and/or embedding. Dimpling of the retractable sheath and/or embedding of the retractable sheath increases the forces required to retract the sheath. Moreover, where thinner sheaths are used, loading a stent may prove difficult as a result of buckling of the sheath.
The problems of dimpling and/or embedding of the stent impact on the choice of materials for sheaths. Materials such as PTFE are desirable for use in retractable sheaths because of their low coefficients of friction, but they are particularly susceptible to dimpling and/or impressing of the stent in the materials and have not, to date, proved practical for use in retractable sheaths.
Although there have been a multitude of patents directed toward stent delivery catheters, there remains a need for innovative catheters which avoid the above-mentioned problems. There also remains a need for catheters having retractable sheaths which are formed using low coefficient of friction materials without the above mentioned disadvantages of such materials.
All U.S. patents and applications and all other published documents mentioned anywhere in this application are incorporated herein by reference in their entirety.
Without limiting the scope of the invention a brief summary of some of the claimed embodiments of the invention is set forth below. Additional details of the summarized embodiments of the invention and/or additional embodiments of the invention may be found in the Detailed Description of the Invention below.
A brief abstract of the technical disclosure in the specification is provided as well only for the purposes of complying with 37 C.F.R. 1.72.
The instant invention is directed in one embodiment to a medical device delivery catheter comprising an inner member and a retractable sheath assembly disposed about the inner member. The retractable sheath assembly comprises an outer sheath of a first material and one or more skids. The skids comprise an outer layer of a first skid material and an inner layer of a second skid material. The second skid material is different from the first skid material. The retractable sheath assembly is constructed and arranged such that the skids are disposed between the outer sheath and the inner member prior to, during and subsequent to retraction of the retractable sheath assembly. Optionally, the catheter further comprises a stent or other medical device disposed about the inner member with the retractable sheath assembly disposed about the stent.
Desirably, the first skid material is harder than the second skid material, desirably as measured using the Shore D hardness scale. Also desirably, the second skid material is more slippery than the first skid material, desirably as measured by the coefficient of friction. Even more desirably, the first skid material is harder than the second skid material and the second skid material is more slippery than the first skid material. As an example of a suitable combination of materials, the first skid material may be a hard polymeric material such as polyimide and the second skid material is a slippery polymeric material such as PTFE. Other suitable materials for the second skid material include ceramics, amorphous carbonxe2x80x94desirably in the form of diamond like coatings and ceramicxe2x80x94for example A1O. The second skid material may line the entire interior of the sheath or may be provided in the form of skids which are adjacent one another and spaced from one another.
In yet another embodiment, the invention is directed to a medical device delivery catheter comprising an inner member and a retractable sheath assembly disposed about the inner member, the retractable sheath assembly having a bending flexibility of at least 1.17 GPa. Desirably, the retractable sheath assembly includes one or more skids. The skids comprise an outer skid layer of a first skid material and an inner skid layer of a second skid material. The outer skid layer may optionally have a shore D hardness of at least 84. The one or more skids are disposed between the sheath and the inner member. Desirably, the retractable sheath assembly further comprises a sheath disposed about the skids and attached thereto.
Additional details and/or embodiments of the invention are discussed below.